A graphic of the location of anchor bolts on the bridge. The faulty 2008 bolts are circled in white. (graphic: Bay Area Toll Authority)

The Metropolitan Transportation Commission (MTC) and Caltrans say they will replace or reinforce all 96 of the 2008 anchor bolts installed in the new eastern span of the Bay Bridge, not just the 30 that have failed so far. Those bolts snapped within days of being tightened this March.

MTC Executive Director Steve Heminger also today unveiled two possible design solutions, down from three, to ensure the seismic safety of the bridge. But Heminger told members of the Bay Area Toll Authority that he couldn’t give a timeline for a repair for another two weeks.

There are plenty of other open questions, too.

One of those is what to do with 192 similar bolts installed on the bridge. This batch was manufactured in 2010 to the same specifications as the ones that gave way. So far none of the 2010 bolts have shown weakness and initial testing seems to suggest they are stronger.

Heminger told commissioners there are quite a few differences between the batches, “but unfortunately quite a few similarities.” For instance, both lots of bolts had the same manufacturer and were built with the same plans. However, Heminger said the materials that went into the 2010 batch were more uniform.

A careful look at the metal in the 2008 rods that show hydrogen embrittlement. (graphic: Bay Area Toll Authority)

Meanwhile, today hydrogen embrittlement was definitively fingered as the cause of the breaking bolts. The responsible party, and likely the one who will have to absorb the cost, is still under investigation.

For one local metallurgist, though, the answer is clear. Yun Chung, a retired Bechtel materials engineer, sent Bay Area transportation leaders a letter that seems to fault Caltrans and the process it used to determine whether the material would be service worthy. He told the San Jose Mercury News that more bolts could still fail if they are not replaced..

“It is very apparent that no one was paying attention to the possibility of hydrogen embrittlement when the rods were in service,” said Chung, who retired 20 years ago and lives in the East Bay. “Instead, they were focused on hydrogen in the production process. From what I see in the documents, Dyson (the manufacturer) gave Caltrans what it asked for. Caltrans fell on its face.”

At today’s meeting, MTC’s Heminger did reiterate that safety prompted the building of the new span, and that’s the singular priority. Officials said that the bridge is being “designed to withstand the greatest ground motions expected over a 1,500-year period.”